The present Invention relates to a method and apparatus for power amplification and a system incorporating the same. The invention is particularly, but not exclusively, intended for use in a wireless communications base station.
Known wireless communications systems require provision of a high power signal for transmission in order to ensure reception over a suitably wide area. This is achieved by amplifying the data signal to be transmitted, typically at a wireless base station itself, and feeding the resulting amplified signal to the antenna array for wireless transmission. The high amplification levels required for such applications can lead to non-linear distortion of the data signal, which is undesirable. It is therefore highly desirable to use high-performance, linear power amplifier architectures in such applications.
A problem with known linear Power Amplifier (PA) technology is that a static back-off, proportional to the signal statistics (Complementary Cumulative Distribution Function (CCDF)), is required to obtain linearity in the system. This back-off decreases the maximum obtainable efficiency of the system and drives mechanical, thermal, and overhead powering costs for wireless transmit architectures. Known techniques yield PA efficiencies in the order of 10-12% for high power designs for signals with high peak-to-mean ratios such as Code Division Multiple Access (CDMA) and Wideband CDMA (W-CDMA). It is therefore desirable to improve the efficiency of power amplifiers so as to reduce operating costs.
Known solutions include Envelope Elimination and Recovery (EER) but such solutions have limited performance due to cross modulation induced by varying the DC voltage applied to the device output. EER cannot be easily incorporated in a wideband architecture since the cross modulation ultimately limits the system linearity and hence limits the ability to meet current standards requirements. Significant memory components are added to the signal envelope at wide bandwidths thus creating an inherently non-linear system.
Power amplifiers today account for a high proportion of wireless Basestation Transmitter System (BTS) costs. In addition, infrastructure support for the power amplifiers (in terms of mechanical, cooling, and DC powering), combined with the basic power amplifiers costs, total a majority of BTS costs. It Is therefore desirable to identify means whereby to reduce installation and/or operating costs of such systems.
The present invention seeks to provide an improved method and apparatus for power amplification and especially for linear power amplification, both in wireless base station applications and elsewhere.
According to a first aspect of the present invention there is provided a power amplifier arrangement comprising: a power amplifier comprising an input port for receiving a data signal and an output port for providing an amplified data signal responsive to the data signal; a power supply arranged to supply power to the power amplifier, the power supply being arranged to be modulated responsive to the data signal.
In a preferred embodiment, the power amplifier further comprises: a predistorter arranged to provide the data signal responsive to receipt of an unpredistorted data signal.
In this context, it will be understood by the skilled person that the unpredistorted signal is unpredistorted relative to the data signal, and does not preclude predistortion for purposes other than the present power amplification.
Advantageously, the predistorter is arranged to correct any non-linearities induced by the power supply modulation, memory components produced as a result of the power supply modulation and the inherent device non-linearities, whereby to provide a substantially linear amplifier performance.
Preferably, the power supply is arranged to be modulated responsive to at least one of the unpredistorted data signal, the data signal, and the amplified data signal.
In another preferred embodiment, the data signal is one of a CDMA signal and a W-CDMA signal. Where predistortion is employed, the data signal in this context will be understood to refer to the unpredistorted signal.
According to a further aspect of the present invention there is provided a power amplifier arrangement comprising: a power amplifier arranged to amplify a data signal; a power supply arranged to provide power to the power amplifier; a power supply modulator arranged to receive the data signal and to modulate the voltage provided by the power supply to the power amplifier responsive to at least one of the data signal, and the amplified data signal.
In a preferred embodiment, the power amplifier arrangement additionally comprises: a predistorter arranged to provide the data signal responsive to receipt of an unpredistorted data signal; and in which the power supply modulator is arranged to modulate the voltage responsive to at least one of the unpredistorted data signal, the data signal, and the amplified data signal.
The invention also provides for a system for the purposes of communications which comprises one or more instances of apparatus embodying the present invention, together with other additional apparatus.
In particular, the invention also provides for a wireless communications base station transmitter, a wireless communications base station, and a communications network comprising such a power amplifier arrangement.
According to a further aspect of the present invention there is provided a power supply modulator arrangement comprising: a first port arranged to receive a data signal; a second port arranged to emit power supply control signals responsive to the data signal; a third port arranged to receive a signal representative of the data signal and the power supply control signals.
The invention is also directed to methods by which the described apparatus operates and including method steps for carrying out every function of the apparatus.
In particular, according to a further aspect of the present invention there is provided a method of amplifying a data signal using a power amplifier having a power supply input, the method comprising the steps of: receiving the data signal; amplifying the data signal using the power amplifier whereby to provide an amplified data signal; modulating the power supply input to the power amplifier responsive the amplified data signal.
According to a further aspect of the present invention there is provided a method of improving power amplifier efficiency comprising the steps of: providing a power amplifier arranged to receive a data signal and to provide an amplified data signal; modulating power supplied to the power amplifier responsive to the amplified data signal.
Other aspects of the invention include software for implementing the amplifier arrangement or for carrying out (which encompasses controlling) the method steps. This acknowledges that such software can be a valuable, separately tradable commodity. Such software is intended to encompass software which runs on or controls xe2x80x9cdumbxe2x80x9d or standard hardware, to carry out the desired functions, (and therefore the software essentially defines the functions of the arrangement). For similar reasons, it is also intended to encompass software (such as HDL (hardware description language) software) which describes or defines the configuration of hardware, as is used for designing silicon chips, or for configuring universal programmable chips, to carry out desired functions.
In particular, according to a further aspect of the present invention there is provided a program for a computer for controlling a power amplifier arrangement comprising a power amplifier and a power amplifier power supply unit, the program comprising code portions arranged to: receive a first signal representative of a data input signal to the power amplifier; receive a signal representative of an data output signal from the power amplifier; control modulation of the power supply responsive to receipt of the first and second signals.
Another aspect provides a method of offering or providing a data transmission service over a network using such a power amplifier. As the advantages of the invention can enable a better network, which is more reliable or more flexible, or has greater capacity, or is more cost effective for example, consequently a data transmission service over the network can show a corresponding improvement, and the value of such services can increase. Such increased value over the life of the system, could prove far greater than the sales value of the equipment.
Advantageously, power amplification costs are improved. Advantageously, the cost of ownership of such equipment to customers is also reduced, both in terms of long term AC power costs and in terms of improved reliability due to reduced thermal loading on the BTS.
The preferred features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the invention.